The folks over at Ham Radio Workbench ( have developed a generic development platform ("Benchduino") that has pluggable CPU daughterboards.

I have developed a daughterboard for the Teensy 4.1 (should also work on the 4.0 version too). The gerbers and the Eagle design files are currently stored in the "Files" section of the "SoftwareControlledHamRadio" :

They are also in the files section of the Ham Radio Workbench Facebook page.

Not 100% tested (i.e. use at your own risk, no warranty, etc. etc....). But let me know if you find any problems.